1. Field of the Invention
This invention relates to a toner for developing an electrostatic image in electrophotography, electrostatic recording, electrostatic printing, etc.
2. Description of the Prior Art
Toners widely used in general have been hitherto produced by dry blending a styrene/acrylate copolymer powder resulting from suspension polymerization with a colorant such as carbon black, and optionally a charge control agent and/or a magnetic material, melt-kneading the blend with an extruder, etc., then pulverizing the resulting blend and classifying the pulverizate (see Japanese Laid-open Patent Application No. 23,354/1976).
The conventional toners obtained by the above method are, however, limited in controlling the particle size of the toners, and toner fine particles can hardly be formed in good yields. Besides, dispersion is nonuniform and electrostatic charge distribution becomes broad. Consequently, when they are used as a developer, there are unavoidable defects in that resolution is low, and fogging, scattering, etc. occur.
Therefor, polymer particle systems improving the above defects and other toner characteristics have been proposed from various purposes. For example, Yamaguchi, et al., U.S. Pat. No. 4,950,573 discloses a toner comprising thermoplastic base particles having a particle size of 5 to 25 micron and small particles having a particle size of not more than one-fourth that of the base particles and containing an organic polymer and colorant; Hedall et al., U.S. Pat. No. 4,794,065 discloses a toner comprising internally pigmented thermo-plastic base particles and thermoplastic fine particles containing a polar polymer wherein said fine particles are on the surface of the base particles; Hasegawa, et al., U.S. Pat. No. 4,996,127 and Masuda et al., Japanese unexamined Patent Publication No. 4-284461 disclose a toner comprising secondary particles which are formed by agglomerating primary particles containing polar polymer and coloring agent.
However, more improvement is demanded for obtaining a toner wherein in preparation of primary particles constituting the toner the yield of desired toner particles is good, and dispersion is uniform and electrostatic charge distribution is narrow, and which is excellent in development characteristics such as resolution and fogging.
Thus, the object of this invention lies in providing a toner for developing an electrostatic image in electrophotography in which toner the yield of desired toner particles is improved and dispersibility of colorants in the toner articles, etc. are improved.